Indium plating



Patented Jan. 16, 1951 INDIUM PLATING David Frederick Green and J olin;E rnest Salmon,'

" ni cn Eng and,

Products Limited London,England' No Dating. Application November 7,1945, se- "rial. No. 627,218. In GreatBritainJanuary- 2,

This invention relates to indium plating particularly in its relation to-electroplating bearing surfaces.

In the specification of our U. S. application Ser. No. 604,524, newPatent No; 2, l9'7,9 88,"dat ed Feb ruary 21, 1950, a stableelectrolytic bath isdescribed which consists of an indium salt, alkalimetal cyanide and hydroxide and dextrose or other suitable saccharide.While other indium salts may be used the use of the chloride ispreferred. Our research has established that it is not necessary to usea saccharide as laid down in our prior specification above referred to,but that other materials such as certain polyhydric alcohols can be usedand sorbitol has been found particularly suitable. The sorbitol can besubstituted for dextrose in the solutions described in our priorspecifications in similar concentrations and solutions so prepared canbe used to prepare a solid residue which can be stored and transportedconveniently and then used to reconstitute a plating solution merely bydissolving in water and adjusting the free alkali metal cyanide andhydroxide contents to the desired concentrations.

Alternatively, if desired, suificient alkali metal cyanide and hydroxidecan be mixed with the solid so that when dissolved in water it willyield a solution containing the desired concentrations of free alkalimetal cyanide and hydroxide. The amount of cyanide and hydroxiderequired can easily be determined by dissolving a small portion of eachbatch in the appropriate quantity of water and analysing the solution.

Our invention may be said to consist of:

An electrolytic bath'for use in electroplating with indium according towhich sufficient alkali metal hydroxide is added toan electrolytic bathconsisting of an indium salt, alkali metal cyanide and sorbitol orequivalent polyhydric alcohol to provide a stable solution,

The invention further comprises a process of electroplating with indiumwherein such an electrolytic bath is used.

Suitable hydroxides for use in the process are sodium or potassiumhydroxide, and the indium salt employed is preferably indium chloride.

One specific electrolytic bath for use in plating metals with indium,according to our invention, consists of a stable composition of indium,potassium cyanide, potassium hydroxide and sorbitol.

According to one method of preparing such an electrolytic bathcomprising indium-potassium cyanide-potassium hydroxide and sorbitol theindium metal is first dissolved in an excess of concentratedhydrochloric acid and the solution evapccl ims. (o1. aura-45)orated-until crystallisation of indium" chloride occurs, andth'ecrystallised indium chloride. is" I then -dissolved in distilled'waterfasecond solu tion 0fpotassium cyanide and sorbitol in water anda:' third solution of potassium-hydroxide in water' arethen-prepared,the first solution is then added to the second solution drop by dropaccompanied by constant stirring and the third solution is then added.The quantities of the materials used being selected to obtain a stablesolution. An example of these quantities which has proved satisfactoryis as follows:

Indium metal, 30 grammes Potassium-cyanide, grammes or approximately 2moles Sorbitol, 30 grammes Potassium hydroxide, grammes or approximately2 moles to make 1 litre of solution.

We claim:

1. A solid soluble mixture adapted to be dissolved in water to producean electrolytic indium plating bath which comprises indium, sorbitol,alkali metal hydroxide and alkali metal cyanide in or about thefollowing proportions: 30 grammes of. indium as indium trichloride, 2moles of alkali metal cyanide, 30 grammes'of sorbitol and approximately2 moles of an alkali metal hydroxide.

2. A solid soluble mixture adapted to be dissolved in water to producean electrolytic indium plating bath which comprises indium, sorbitol,potassium hydroxide and potassium cyanide in or about the followingproportions; 30 grammes of indium as indium trichloride, 30 grammes ofsorbitol, 100 grammes of potassium cyanide and 120 grammes of potassiumhydroxide.

3. A solid soluble mixture adapted to be dissolved in water to producean electrolytic indium plating bath which comprises indium, sorbitol,sodium hydroxide and sodium cyanide in or about the followingproportions: 30 grammes of indium as indium trichloride, 30 grammes ofsorbitol, 2 moles of sodium hydroxide and 2 moles of sodium cyanide.

4. Amethod of making a water soluble mixture for use in preparing anindium electroplating bath according to which 30 grammes of indium asindium trichloride is added to a solution containing approximately 2moles of alkali metal cyanide and 30 grammes of sorbitol andapproximately 2 moles of an alkali metal hydroxide in which the indiumsolution is added to a mixture of the sorbitol and cyanide accompaniedby agita- 3 tion and subsequently the hydroxide is added and thesolution is evaporated to dryness to leave a residue soluble in water,

5. A method of making a water soluble mixture for use in preparing anindium electroplating bath according to which 30 grammes of indium asindium trichloride is added to a solution containing approximately 100grammes of potassium cyanide and 30 grammes of sorbitol and ap-'proximately 120 grammes of potassium hydroxide in which the indiumsolution is added to a mixture of the sorbitol and cyanide accompaniedby agitation and subsequently the hydroxide is added and the solution isevaporated to dryness to leave a residue soluble in water. v

6. A method of making a water soluble mixture for use in preparing anindium electroplating bath according to which 30 grammes of indium asindium trichloride is added to a solution containing approximately 2moles of sodium cyanide and 30 grammes of sorbitol and approximately 2moles of sodium hydroxide in which the indium solution is added to amixture of the sorbitol and cyanide accompanied by agitation andsubsequently the hydroxide is added and the solution is evaporated todryness to leave a residue soluble in water.

DAVID FREDERICK GREEN. JOHN ERNEST SALMON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 694,658 Meurant Mar. 4, 19021,849,293 Gray Mar. 15, 1932 1,965,251" Murray et a1. July 3, 19342,423,624 Smart July 8, 1947 2,458,839 Dyer et a1 Jan. 11, 1949 VFOREIGN PATENTS Number Country Date 573,848 Great Britain of 1945 OTHERREFERENCES Iron Age, Dec. 19, 1940, pp. 35-38, Transactions ofElectrochemical Society, vol. 65, pp. 377-383 (1934).

1. A SOLID SOLUBLE MIXTURE ADAPTED TO BE DISSOLVED IN WATER TO PRODUCEAN ELECTROLYTIC INDIUM PLATING BATH WHICH COMPRISES INDIUM, SORBITOL,ALKALI METAL HYDROXIDE AND ALKALI METAL CYANIDE IN OR ABOUT THEFOLLOWING PROPORTIONS: 30 GRAMMES OF INDIUM OF INDUIM TRICHLORIDE, 2MOLES AND APPROXIMATELY 2 MOLES OF AN ALKALI METAL HYDROXIDE.